KR101512711B1 - Retardation film and wideviewing twist nematic liquid crystal display comprising the same - Google Patents

Abstract

The present invention relates to a polarizing plate comprising a substrate layer having a specific optical property and a discotic liquid crystal coating layer and a polarizing plate laminated with the retardation film to completely realize a black state in a full- And a twisted nematic (TN) mode liquid crystal display device capable of securing a wide viewing angle.

A liquid crystal display, a polarizing plate, a discotic liquid crystal coating layer

Description

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a retardation film and a wide viewing angle twisted nematic mode liquid crystal display including the retardation film,

The present invention relates to a liquid crystal display device and a method of manufacturing the liquid crystal display device, which are capable of realizing a black state at all viewing angles in a state in which a voltage is applied, (Hereinafter referred to as " TN ") mode liquid crystal display device.

2. Description of the Related Art A liquid crystal display (LCD) is widely used as a popular image display device. However, despite its many excellent properties, a narrow viewing angle has been pointed out as a typical drawback. A technology for securing a wide viewing angle by applying a functional optical film such as a retardation film has appeared, and new liquid crystal modes capable of realizing a wide viewing angle technology without using a functional optical film in an initial TN (Twisted Nematic) mode Was presented.

The liquid crystal display device requires a polarizing plate for polarizing light on both sides of the liquid crystal cell. Generally, the polarizing plate has a protective film on both sides with a polarizer as a center, and a liquid crystal cell has a functional film such as a retardation film Is used additionally. In recent years, the retardation film generally serves not only as a viewing angle compensation but also as a protective film.

On the other hand, the TN mode has a form in which the liquid crystal is twisted by 90 degrees when no voltage is applied, and the liquid crystal is vertically aligned between the upper and lower substrates when a voltage is applied. However, even when a voltage is applied, liquid crystals located close to the substrate exist liquid crystals that can not be vertically aligned with respect to the liquid crystal substrate, which is the largest (lowest) image quality at the slope when displaying the BLACK in TN mode . In order to compensate for the liquid crystal located close to the substrate which is not vertically oriented when displaying the black (black), a film coated with a discotic liquid crystal on a triacetyl cellulose (TAC) used as a protective layer of a polarizer is used, The liquid crystal has a tilt angle in one direction. Although the viewing angle compensation is implemented by tilting the discotic liquid crystal, it is impossible to realize a complete black state simply by tilting the discotic liquid crystal.

The present invention is intended to solve the problem that a conventional TN mode liquid crystal display device to which a film coated with a discotic liquid crystal is applied is difficult to realize a complete black state. It has been found that the conventional TN mode liquid crystal display device is generated because the coating film of the discotic liquid crystal performs only compensation for the TN liquid crystal cell and does not simultaneously compensate for the TN liquid crystal cell and the axis (absorption axis) .

Accordingly, the present invention accurately models and analyzes the liquid crystal behavior of the TN liquid crystal cell layer when a voltage is applied, and a phase difference film including a base layer having a specific optical property and a discotic liquid crystal layer is formed on one side of the polarizer (TN) mode liquid crystal display device comprising a polarizing plate to which the retardation film is applied, the polarizing plate including a top plate and a bottom plate, the twin nematic To achieve a perfect black state in all directions.

A retardation film comprising a base layer and a discotic liquid crystal coating layer, wherein the base layer has a front retardation of 60 to 90 nm and a refractive index ratio (NZ) of 1.5 < NZ < 1.9, And is configured to be orthogonal to the axis; Wherein the discotic liquid crystal coating layer has an oblique retardation (R ₄₀ ) of 7 to 13 nm and 55 to 85 nm when the front phase difference is 30 to 50 nm and a slow axis is a rotation axis, and an oblique retardation (R ₄₀ ) And 45 nm.

In addition, the present invention is further characterized in that the polarizing plate in which the retardation film is laminated on the TN liquid crystal cell side of the polarizer.

The present invention is further characterized by a liquid crystal display device including the polarizer plate as an upper plate and a lower plate polarizer.

The twisted nematic mode liquid crystal display device according to the present invention can be manufactured by applying a retardation film including a substrate layer having a specific optical property and a discotic liquid crystal layer, accurately modeling the liquid crystal behavior of the liquid crystal cell layer and performing optical analysis, A wide viewing angle and a high contrast ratio (CR) can be achieved by making it possible to realize a perfect black state in all directions by reducing the total amount of light.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film capable of compensating for a TN liquid crystal cell and compensating an absorption axis simultaneously when applied to a twisted nematic mode liquid crystal display device, thereby achieving a dark state at a wide viewing angle. The retardation film is made of a base layer and a discotic liquid crystal coating layer, wherein the base layer has a front retardation of 60 to 90 nm and 1.5 < NZ < 1.9 and the direction of the slow axis is orthogonal to the absorption axis of the adjacent polarizer, The liquid crystal coating layer has a front retardation of 30 to 50 nm and an oblique retardation (R ₄₀ ) of 7 to 13 nm and 55 to 85 nm when the retardation axis is a rotation axis and an oblique retardation (R ₄₀ ) of 25 to 45 nm .

In general, when a voltage is applied to a TN mode liquid crystal display device, a wide viewing angle can be secured by implementing a black in a full field of view. For this purpose, it is better to define the exact direction of the TN liquid crystal cell when the voltage is applied in the currently produced TN liquid crystal cell. Specifically, when the TN liquid crystal cell displays black, the liquid crystal direction is defined by dividing the TN liquid crystal cell into a plurality of layers in the thickness direction and expressing the liquid crystal direction of each layer in three dimensions.

In addition, in order to define the liquid crystal direction in the BLACK state of the TN liquid crystal cell, the TN liquid crystal cell can be calculated by changing the incident angle and measuring the phase difference while applying the voltage to the TN liquid crystal cell. FIGS. 3 and 4 illustrate the directions of liquid crystals based on the result of measuring the retardation of the TN liquid crystal cell in various directions. The factors affecting the calculated values are the dielectric constant, the elastic modulus, and the viscosity. 3 is a graph showing the tilt angle of each layer when the liquid crystal is divided into 40 layers in the thickness direction in a state where a voltage is applied. The tilt angle refers to the angle formed by the major axis direction of the liquid crystal with the surface of the liquid crystal as shown in FIG. 5, and it is found that the tilt angle corresponds to 90-theta value in the coordinate system in which the Z axis in FIG. . Fig. 4 shows the direction angle of the liquid crystal in a state in which the voltage is applied, and the direction angle coincides with? In Fig.

By inputting and applying the information of the TN liquid crystal cell into the LCD optical simulation program (e.g., LCD Master, Techwiz LCD 1D) under the above-defined BLACK condition, Black) state can be perfectly implemented to enable the design of a composite polarizing plate (retardation film + polarizer) capable of securing a wide viewing angle.

In the case of the TN mode liquid crystal display device, the absorption axes of the lower plate polarizer and the upper polarizer are positioned in a diagonal direction not perpendicular or horizontal when viewed from the front. When the absorption axes of the lower polarizer and the upper polarizer are perpendicular to each other, Mode, and when they are parallel to each other, it is called NB (Normal Black) mode. In the normal case, the TN mode is the NW (Normal White) mode, and the TN mode of the present invention is also the 'NW (Normal White) mode'. When the rubbing angle of the substrate adjacent to the absorption axis of the polarizing plate in the TN mode is parallel to each other, the O-mode is referred to as an E-mode. In the present invention, the TN-LCD is limited to the 'O-mode'. That is, the TN mode in the present invention is limited to the range of 'NW (Normal Wite) mode' and 'O-mode'. However, it can be seen that the conventional NW (Normal Wite) mode and the O-mode TN mode liquid crystal display have poor image quality due to light leakage in the black state. In addition, when a polarizer is attached to a TN liquid crystal cell and the voltage is applied, as shown in the result of FIG. 8, which is the transmittance, a large amount of light leaks in the directions of?> 20 degrees and in the directions of 0 degrees, 90 degrees, 180 degrees, .

If the change of the polarization state due to the phase difference is understood and the Poincare Shpere is expressed, it is possible to design a phase difference that widens the viewing angle. This is because the optical principle of the viewing angle compensation technique do. However, the point S3 (1,0,0,1) on the Poincare Shpere in the present invention is the right circularly polarized light and the reference on the Poincare Sphere for [theta] and [phi] And the right side is turned toward the observer by &amp;thetas;

That is, the present invention precisely models the liquid crystal behavior of the TN liquid crystal cell layer and clearly analyzes the change of the polarization state according to the retardation so that the retardation film can be applied to the retardation film .

When the base layer constituting the retardation film of the present invention has a frontal retardation of 60 to 90 nm and maintains a refractive index ratio of 1.5 < NZ < 1.9 and exhibits better optical characteristics of right and left viewing angle expansion, To 80 nm and a refractive index ratio of 1.6 < NZ < 1.8, and the direction of the slow axis is orthogonal to the absorption axis of the adjacent polarizer. At this time, the base layer may be produced by a material commonly used in the art to which a retardation is imparted by stretching, and any material can be used as long as it can satisfy the optical properties of the front retardation and the refractive index ratio. Specifically, the material forming the base layer may be selected from the group consisting of triacetylcellulose (TAC), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), polypropylene (PP), polycarbonate Polysulfone (PSF) and polymethyl methacrylate (PMMA) can be used.

The discotic liquid crystal coating layer constituting the retardation film has a front retardation of 30 to 50 nm and an oblique retardation (R ₄₀ ) of 7 to 13 nm and 55 to 85 nm when the retardation axis is the rotation axis and an oblique retardation (R ₄₀ may be 25 to 45 nm, preferably a frontal retardation of 35 to 45 nm, an inclined phase difference (R ₄₀ ) of 8 to 12 nm and a radius of 60 to 80 nm when the slow axis is the rotation axis, It is preferable to use an inclined phase difference (R ₄₀ ) of 30 to 40 nm. At this time, the inclined phase difference (R ₄₀ ), which is generally defined in the art, represents the phase difference when tilted at ± 40 degrees. That is, when the ground shaft is the rotation axis, the inclination phase difference (R ₄₀ ) is the phase difference value when the ground shaft is tilted at ± 40 ° with the rotation axis, and when the leading axis is the rotation axis, the inclination phase difference (R ₄₀ ) Represents the phase difference value when tilted at 40 degrees.

Preferably, the thickness of the discotic liquid crystal coating layer is 0.1 to 10 占 퐉, the refractive index difference? N = ne-no of the liquid crystal is -0.5 to -0.03, and the tilt angle of the surface portion of the discotic liquid crystal coating layer is about 80 It is better to use a liquid crystal that can be coated to a wide range.

The slow axis of each of the base layer and the discotic liquid crystal coating layer constituting the retardation film is configured to be orthogonal to the absorption axis of the adjacent polarizer.

According to the present invention, a polarizing plate is constructed by including a retardation film obtained by analyzing a liquid crystal behavior of a TN liquid crystal cell layer and a change in polarization state according to a retardation. At this time, the retardation film may be laminated on the side of the liquid crystal cell of the polarizer, and triacetyl cellulose (TAC) may be laminated on the other side of the polarizer opposite to the liquid crystal cell.

Further, a TN mode liquid crystal display device is constructed by including the polarizer plate in which the retardation film is laminated as an upper plate and a lower plate polarizer. The polarizing plate may be formed by laminating a phase difference film having the same optical properties as those of the upper plate and the lower plate or by laminating different retardation films having optical properties satisfying the range of the present invention.

The optical properties of the base layer and the discotic liquid crystal coating layer constituting the retardation film and the polarizing plate are as shown in Fig. 7, when the thickness direction is the z axis, the direction in which the in-plane refractive index is large is the x axis and the perpendicular direction is the y axis And Nx, Ny, and Nz, refractive indices corresponding to the respective directions are expressed by the following equations (1) and (2), the retardation value R0 defined by the following equation (2) Is defined by the defined refractive index ratio (NZ).

R0 = (Nx - Ny) xd

(Where Nx and Ny are the surface refractive indexes of the retardation film and d is the thickness of the film, where Nx &gt; = Ny)

Rth = [(Nx + Ny) / 2-Nz] xd

(Where Nx and Ny are surface refractive indices Nx &gt; = Ny, Nz is refractive index in the thickness direction of the film, and d is the thickness of the film)

NZ = (Nx - Nz) / (Nx - Ny) = Rth / R0 + 0.5

(Where Nx and Ny are surface refractive indices Nx &gt; = Ny, Nz is refractive index in the thickness direction of the film, and d is the thickness of the film)

1 is a perspective view illustrating a basic structure of a TN mode liquid crystal display device according to an exemplary embodiment of the present invention. Referring to FIG.

The TN mode liquid crystal display device according to the present invention includes a lower polarizer plate 10, a liquid crystal cell 30 and a top polarizer plate 20 laminated in this order from the backlight unit side 40 to the lower polarizer plate 10 and the upper plate polarizer 20 The protective films TAC 13 and 23 are located on the opposite sides of the liquid crystal cell of the polarizers 11 and 21 of the polarizer 11 and the substrate layer 14 and the discotic liquid crystal coating layer 16 ). At this time, the retardation films 50 and 60 are laminated on the upper plate and the lower plate polarizer.

More specifically, the liquid crystal cell 30 having a twist angle of about 90 degrees with positive dielectric anisotropy (??> 0) between the lower plate polarizer 10 and the two glass substrates and the upper plate polarizer 20 And an active matrix drive electrode including an electrode pair is formed on the adjacent surface of the liquid crystal cell 30 on the glass substrate of the liquid crystal cell 30, So that the direction of the liquid crystal changes in the vertical direction. The liquid crystal cell has the liquid crystal alignment direction of the backlight side liquid crystal substrate at 135 degrees with respect to the horizontal direction when viewed from the viewer side, and the liquid crystal alignment direction of the liquid crystal substrate at the viewer side is at 45 degrees.

The absorption axis 12 of the lower plate polarizer 10 and the absorption axis 22 of the upper plate polarizer 20 are orthogonal to each other and the absorption axis 12 of the lower polarizer 10 is positioned on the viewer side And the absorption axes 12 and 22 of the polarizers 10 and 20 are positioned at 135 degrees with respect to the horizontal direction of the liquid crystal substrate on the backlight side in the liquid crystal alignment direction of the adjacent liquid crystal cell, ). When the voltage is applied to the liquid crystal cell 30, the direction of the liquid crystal becomes more difficult to vertically align due to the voltage as it is closer to the substrate of the liquid crystal cell 30, which is the main reason for degrading the image quality in the black state.

The liquid crystal cell 30 has a panel retardation value (DELTA n x d) defined by Equation (4) is approximately 400 nm at a wavelength of 589 nm. This is because, in a state where no voltage is applied to the TN-LCD panel, the linearly polarized light passing through the lower plate polarizer 10 in the front side of the viewer side passes through the liquid crystal cell 30 and is rotated by 90 degrees, This is because the retardation value of the liquid crystal cell 30 of the TN-LCD panel must be sufficiently large at the light source of 589 nm in order to be in the bright state in agreement with the transmission axis.

Δn × d = (ne-no) × d

(Where ne is the extraordinary ray refraction index of the liquid crystal, no is the normal ray refraction index, d is the cell gap, note Δn, d is not a vector)

The base layers 14 and 24 constituting the retardation film are each configured so that the frontal retardation is 60 to 90 nm, the refractive index ratio is 1.5 <NZ <1.9, and the direction of the slow axis is orthogonal to the absorption axis of the adjacent polarizer. The base layers 14 and 24 have a property of increasing the refractive index with respect to the stretching direction. When the direction in which the film is wound on the roll is referred to as the machine direction (Machine Direction), as shown in Fig. 9, (NZ) of the formula (3), and the slow axes 15 and 25 are formed in the stretching direction. A discotic liquid crystal coating layer is added to the substrate layer by stretching at the substrate end, and the polarizing plate is bonded to a PVA polarizer and a protective film (TAC), and then cut in a diagonal direction to form a composite polarizing plate applicable to the present invention. And the present invention is not limited thereto. Such a series of processes can be manufactured in the form of a roll-to-roll (roll-to-roll) system.

The discotic liquid crystal coating layers 16 and 26 have an oblique phase difference R _{40 of} 7 to 13 nm and 55 to 85 nm when the front phase difference is 30 to 50 nm and the slow axis is the rotation axis, R ₄₀ ) of 25 to 45 nm can be used. Such a retardation film including a base layer having a specific optical property and a discotic liquid crystal layer corresponds to both the upper plate and the lower plate polarizer.

The principle of compensating the viewing angle of the present invention can be expressed by the Poincare Sphere. In general, in the case of a liquid crystal display (IPS-LCD) or a vertical alignment liquid crystal display (VA-LCD), the liquid crystal shape is symmetrical with time when no voltage is applied, can do. However, when a black voltage is applied to the TN-LCD, the liquid crystal adjacent to the substrate of the liquid crystal cell 30 is not vertically aligned but has a low tilt angle. The shape of the liquid crystal changes asymmetrically, so that the compensation principle at a specific time can not be expanded from another viewpoint. In the case of TN-LCD, it is necessary to perform a viewing angle compensation design at each viewing angle. The present invention is applicable to all TN-LCDs using 486nm, 589nm, and 656nm polarizing state change and omnidirectional transmittance on the Poincare sphere of TN- It is possible to realize a complete black state in the direction of the arrow. The twisted nematic mode liquid crystal display device constituted by the optical conditions of the present invention satisfies the compensation relationship of the maximum visual sensitivity transmittance of 1% or less, preferably 0.5% or less.

Hereinafter, the effects of achieving the dark state at the full viewing angle when the voltage is applied according to the above configuration are summarized in the embodiment and the comparative example. The present invention can be better understood by the following examples, and the following examples are intended to illustrate the present invention and are not intended to limit the scope of protection defined by the appended claims.

Example

In Examples 1 to 4 and Comparative Examples 1 to 4, the liquid crystal cell parameters of the LTM220M1-L01 (Samsung Electronics), which is a TN-LCD panel, were applied to an LCD simulation program TECH WIZ LCD 1D (manai system, KOREA) Compare the viewing angle effects.

Example 1

Actual data such as each optical film, liquid crystal cell, and backlight according to the present invention is laminated on a TECH WIZ LCD 1D (MANAMA SYSTEM, KOREA) with the structure shown in FIG. The structure of FIG. 1 will be described in detail as follows.

More specifically, the lower plate polarizer 10 is a laminate of a backlight unit 40 , a lower plate polarizer 10, a liquid crystal cell 30 and a top plate polarizer 20 in this order. 13, a PVA polarizer 11, a base layer 14 and a discotic liquid crystal coating layer 16 in this order. The top plate polarizer is composed of a discotic liquid crystal coating layer 26, a base layer 24, a PVA polarizer (21), and a protective film (23).

The polarizing plates 10 and 20 obtained by laminating the TAC 13 and the protection film 23 on one side of the PVA 11 with the polarizer function 21 are laminated on both sides of the TN mode liquid crystal panel 30, 12) 22 are arranged orthogonally to each other. The alignment direction of the liquid crystal in the TN mode liquid crystal cell 30 is oriented at 31 on the backlight side substrate and 32 on the viewing side substrate when viewed from the viewer side with reference to the direction shown in Fig. The absorption axes 12 and 22 of the substrate-side polarizing plate and the liquid crystal alignment direction are arranged in parallel. The tilt angle of the liquid crystal at the time of voltage application can be calculated by the retardation value in various directions and the normal refractive index and the extraordinary refractive index of the liquid crystal, and is divided into 40 layers in the thickness direction as shown in FIGS. 3 and 4 The direction of the liquid crystal defined in the layer of the layer is parameterized. At this time, a base layer 14 (24) and a discotic liquid crystal coating layer 16 (26) are positioned between the PVA 11 (21) and the liquid crystal cell 30 of each polarizing plate, 25 are orthogonal to the PVA absorption axis 12 and 22 and the liquid crystal cell 30 has a color filter for convenience of simulation Were used.

 Detailed optical properties of each optical film and backlight used in the above examples were used as defined below.

라고 할 때 하기 수학식 5 내지 9에 의해 정의된다.First, polarizers 11 and 21 of the lower plate polarizer 10 and the upper plate polarizer 20 impart a polarizer function by dyeing iodine to the stretched PVA. The polarization performance of the polarizer is such that the visual sensitivity A degree of polarization of 99.9% or more, and a visible light transmittance of 41% or more. The transmittance of the transmission axis according to the wavelength is denoted by TD (λ), the transmittance of the absorption axis with respect to wavelength is denoted by MD (λ), and the visibility correction value defined in JIS Z 8701: 1999

And is defined by the following equations (5) to (9).

The optical characteristics of the TAC, which is the protective layer of the polarizers 10 and 20, are Nx = Ny> Nz when the refractive indexes corresponding to the respective axes are Nx, Ny, and Nz and the thickness is d for the orthogonal coordinate system having the thickness direction as the z- Nz, and 50 nm in the case of Rth of TAC (13) (23) with respect to incident light of 589.3 nm.

The base layers 14 and 24 of the lower and upper polarizers were stretched to give a front retardation of 75 nm and a refractive index ratio NZ = 1.7. The discotic liquid crystal coating layer 16 of the lower plate polarizing plate has a retardation of 10 nm when the front retardation is 40 nm and a direction of -45 degrees with respect to the slow axis 17 is rotated 40 degrees to the direction of the observer, The phase difference is 70 nm when rotated 40 degrees and the 45 degree direction is rotated 40 degrees near the observer direction and the -135 degree direction is rotated 40 degrees near the observer direction with the vertical axis of the slow axis 17 as the rotation axis And the phase difference was 35 nm. The obliquely oriented discotic liquid crystal coating layer 26 of the upper plate polarizing plate has a retardation of 10 nm when the frontal retardation is 40 nm and a retardation angle of 45 ° toward the observer direction with the slow axis 27 as the rotation axis and the direction of -135 degrees is closer to the observer direction , The phase difference was 70 nm, and the vertical axis of the slow axis 27 was used as the rotation axis, and the slopes were oriented so as to be 35 nm when rotated in different directions.

As the backlight unit 40, backlight actual data mounted on the TN-LCD panel LTM220M1-L01 (Samsung Electronics) was used.

As a result of simulating the visibility transmittance of each optical element as shown in Fig. 1 and performing the simulation of the visual sensitivity omnidirectional transmittance, a low transmittance in all directions in the black state is calculated as shown in the right side of Fig. 14, 10 (right), 10 (right), 12 (left), and 13 (left) In the right side.

In the polarized state 1, the polarizer passes through the lower plate polarizing plate. In the polarizing state 2, the base plate passes through the base plate passing through the lower plate polarizing plate. Polarized state 3 is passed through the discotic liquid crystal coating layer of the lower plate polarizer, the liquid crystal passes through the black state in the polarized state 4, and passes through the discotic liquid crystal coating layer of the upper plate polarizer 5 and the base layer And shows the state of polarization after passing. These figures show that when the light passing through the lower plate polarizer passes through the optical system in which the light in the state of polarization 1 is sequentially stacked and finally passes through the base layer of the top plate polarizer, it converges to a point symmetric about the S2 axis on the Poincare Sphere And the degree of convergence in Example 1 (right side) is higher than the degree of convergence in Comparative Example 1 (left side). As a result of such axial compensation, the degree of light leakage in the black state when viewed from the right side, the upper side, the left side, and the lower side is significantly lower than that of Comparative Example 1.

Example 2

The discotic liquid crystal coating layer 26 of the upper plate polarizing plate had a front retardation of 35 nm and a phase difference of 45 degrees when the observer's direction was rotated by 40 degrees with the slow axis 27 as a rotation axis. When the direction of 8.6 nm and -135 degrees was rotated 40 degrees to the direction of the observer, the phase difference was 61.2 nm, and the -45 degree direction was rotated by 40 degrees toward the observer direction with the vertical axis of the ground axis (27) And when the direction of 135 degrees was rotated 40 degrees to the direction of the observer, the twisted nematic liquid crystal display device was manufactured by obliquely aligning so that the retardation was 30.6 nm.

The twisted nematic liquid crystal display device manufactured as described above has an omnidirectional visible transmittance as shown in FIG. 15, and has a wide range of low blue transmittance. Thus, it is possible to realize a wide viewing angle. I can confirm that this is possible.

Example 3

A twisted nematic liquid crystal display device was manufactured in the same manner as in Example 1 except that the substrate layer 24 having a front retardation of 70 nm and an NZ of 1.7 was used as the upper plate polarizer.

FIG. 16 shows a twisted nematic liquid crystal display manufactured according to the present invention. As shown in FIG. 16, a wide viewing angle range can be realized by providing a wide range of low blue transmittance. .

Example 4

The discotic liquid crystal coating layer 26 of the upper plate polarizing plate had a front retardation of 33.1 nm and a retardation of 45 degrees with the slow axis 27 as the axis of rotation and a retardation of 40 degrees near the observer's direction When the direction of 8.3 nm and -135 degrees was rotated 40 degrees to the direction of the observer, the phase difference was 58.0 nm and the -45 degree direction was rotated 40 degrees toward the observer's direction with the vertical direction (fast axis) of the slow axis 27 as the rotation axis And when the direction of 135 degrees was rotated 40 degrees close to the direction of the observer, the twisted nematic liquid crystal display device was manufactured by obliquely aligning so that the phase difference became 29.0 nm.

The twisted nematic liquid crystal display manufactured as described above has an omnidirectional visible transmittance as shown in FIG. 17, and has a wide range of low blue transmittance. Thus, it is possible to realize a wide viewing angle. I can confirm that this is possible.

Example 5

A twisted nematic liquid crystal display device was manufactured in the same manner as in Example 1 except that the substrate layer 24 having a front retardation of 65 nm and NZ of 1.55 was used as a top plate polarizer.

FIG. 18 shows a twisted nematic liquid crystal display fabricated in the above. From this, it is possible to realize a wider viewing angle by broadening the area having a low transmittance at the center (blue), and to realize a dark state at all viewing angles in all directions .

Comparative Example 1

A twisted nematic liquid crystal display device was manufactured in the same manner as in Example 1 except that the front phase difference RO of each of the base layers 14 and 24 was 0 nm and the thickness direction retardation Rth was 110 nm.

The transmittance of the twisted nematic liquid crystal display fabricated as described above is as shown in Fig. 14, which shows that the polarizations of the respective polarizations (right, left, 14 (left) because the change in the state shows the same behavior as that of Comparative Example 1 (left) in Fig. 10 (right), Fig. 11 (left), Fig. 12 It was confirmed that it is impossible to implement a perfect black state.

Comparative Example 2

The discotic liquid crystal coating layer 26 of the upper plate polarizing plate had a frontal phase difference (RO) of 56 nm and a 45-degree direction with the slow axis 27 as a rotation axis was rotated 40 degrees close to the observer's direction When the phase difference is 14 nm and the -135 degree direction is rotated 40 degrees to the direction of the observer, the phase difference is 98 nm and the -45 degree direction is rotated 40 degrees toward the observer direction with the vertical direction (fast axis) of the slow axis 27 as the rotation axis And when the direction of 135 degrees was rotated 40 degrees to the direction of the observer, the twisted nematic liquid crystal display device was manufactured by tilting alignment so that the phase difference was 49 nm.

The transmittance of the twisted nematic liquid crystal display manufactured as described above is shown in FIG. 19, and it can be confirmed that it is impossible to realize a perfect black state in all directions.

Comparative Example 3

The discotic liquid crystal coating layer 16 of the lower plate polarizer was rotated in the direction of -45 degrees toward the observer side by 40 degrees with the frontal phase difference RO of 56 nm and the slow axis 17 as the rotation axis. When the phase difference is 14 nm and the 135 degree direction is rotated 40 degrees to the observer direction and the phase difference is 98 nm and the 45 degree direction is rotated 40 degrees toward the observer direction with the vertical direction (fast axis) of the slow axis 17 as the rotation axis And a phase difference of 49 nm when the direction of -135 degrees was rotated 40 degrees to the direction of the observer, thereby manufacturing a twisted nematic liquid crystal display device.

The transmittance of the twisted nematic liquid crystal display manufactured as described above is shown in FIG. 20, and it can be confirmed that it is impossible to realize a perfect black state in all directions.

Comparative Example 4

A twisted nematic liquid crystal display device was fabricated in the same manner as in Example 1 except that the base layer 24 of the upper polarizer plate had a front retardation (RO) of 100 nm and a refractive index ratio NZ of 2.5.

The transmittance of the twisted nematic liquid crystal display manufactured as described above is shown in FIG. 21, and it can be confirmed that it is impossible to realize a perfect black state in all directions.

As shown above, in the examples and comparative examples, it was found through the Poincare Sphere expression that the substrate layer and the discotic liquid crystal layer had the effect of improving the viewing angle only when they had specific optical properties, It was confirmed that light leakage occurs when the characteristic range is exceeded.

As described above, the twisted nematic liquid crystal display device to which the retardation film according to the present invention is applied can provide excellent image quality for all viewing angles, and can be applied to a liquid crystal display requiring high viewing angle characteristics.

1 is a perspective view exemplarily showing the structure of a TN mode liquid crystal display device including a retardation film according to the present invention,

2 is a view showing a liquid crystal direction 31 adjacent to the substrate on the lower plate polarizing plate side, a liquid crystal direction 32 adjacent to the substrate on the upper plate polarizing plate side, an absorption axis 12 of the lower plate polarizing plate and the upper plate polarizing plate 12 ) 22, and Fig.

3 is a graph showing a tilt angle of a liquid crystal when a voltage is applied to a liquid crystal cell of a TN mode liquid crystal display device,

4 is a graph showing a direction angle of a liquid crystal when a voltage is applied to a liquid crystal cell of a TN mode liquid crystal display device,

5 is a schematic view for explaining the definition of the tilt angle of the liquid crystal,

6 is a schematic view for explaining the direction of the line of sight when the liquid crystal display device is viewed from the viewer side in the present invention by? And? In the circular coordinate system,

7 is a schematic view for explaining the refractive index direction of the retardation film according to the present invention,

8 shows the results of the omni-directional transmittance when the liquid crystal cell 30 is applied with a voltage and only the polarizers 11 and 21 of Fig. 1 are disposed.

9 is a schematic view showing the MD direction in a manufacturing process of a roll film according to the present invention,

10 is a graph showing the viewing angle compensation according to the first embodiment of the present invention on a Poincare Sphere in the direction of? = 60 degrees and? = 0 degrees as compared with Comparative Example 1,

11 is a view on the Poincare Sphere in the direction of? = 60 degrees and? = 90 degrees as compared with Comparative Example 1 in the viewing angle compensation according to Embodiment 1 of the present invention,

12 is a view on the Poincare Sphere in the direction of? = 60 degrees and? = 180 degrees as compared with Comparative Example 1, according to Embodiment 1 of the present invention,

13 is a view on the Poincare Sphere in the direction of? = 60 degrees and? = 270 degrees as compared with Comparative Example 1 in the viewing angle compensation according to Embodiment 1 of the present invention,

Fig. 14 shows omnidirectional transmittance by comparing viewing angle compensation according to Example 1 of the present invention with Comparative Example 1,

15 is a diagram showing a visual sensitivity transmittance according to Example 2 of the present invention,

16 is a view showing an omnidirectional transmittance according to Example 3 of the present invention,

17 shows the visual sensitivity front-end transmission according to the fourth embodiment of the present invention,

18 shows the visual sensitivity front-end transmission according to the fifth embodiment of the present invention,

Fig. 19 shows the visual sensitivity transmittance according to Comparative Example 2 of the present invention,

Fig. 20 shows the visual sensitivity transmittance according to Comparative Example 3 of the present invention,

21 shows the visibility transmittance in all directions according to Comparative Example 4 of the present invention.

Claims (10)

A retardation film comprising a substrate layer and a discotic liquid crystal coating layer, wherein, when a wavelength of 589.3 nm is referred to, Wherein the refractive index ratio (NZ) defined by the following formula (3) is 1.5 < NZ < 1.9, and the direction of the slow axis is orthogonal to the absorption axis of the adjacent polarizer; The discotic liquid crystal coating layer has a retardation value of 7 to 13 nm when the front phase difference is 30 to 50 nm and an inclined phase difference R ₄₀ is ₄₀ degrees to the direction of -45 ° when the slow axis is the rotation axis, Wherein the retardation value is 55 to 85 nm when the retardation film is rotated 40 degrees to the observer's direction and the oblique retardation (R ₄₀ ) is 25 to 45 nm when the retardation axis is the rotation axis. &Quot; (3) &quot; NZ = (Nx - Nz) / (Nx - Ny) = Rth / R0 + 0.5 (Where the thickness direction is the z axis, the direction in which the in-plane refractive index is large is the x axis and the perpendicular direction is the y axis, Nx and Ny are the surface refractive indexes of the retardation film, Nx &gt; = Ny, and Nz is the refractive index and d is the thickness of the film. The phase retardation value R0 and the retardation in thickness direction Rth are specified by the following equations (1) and (2). [Equation 1] R0 = (Nx - Ny) xd (Where Nx and Ny are the surface refractive indexes of the retardation film and d is the thickness of the film, where Nx &gt; = Ny) &Quot; (2) &quot; Rth = [(Nx + Ny) / 2-Nz] xd (Where Nx and Ny are surface refractive indices Nx &gt; = Ny, Nz is refractive index in the thickness direction of the film, and d is the thickness of the film) The method of claim 1, wherein the substrate layer is selected from the group consisting of Triacetyl Cellulose (TAC), Cycloolefin Polymer (COP), Cycloolefin Copolymer (COC), Polyethylene Terephthalate (PET), Polypropylene (PP), Polycarbonate (PSF), and polymethyl methacrylate (PMMA). The retardation film according to claim 1, wherein the retardation of the base layer is given by stretching. Wherein the retardation film of claim 1 is laminated on the side of the TN liquid crystal cell of the polarizer. The polarizing plate according to claim 4, wherein triacetyl cellulose (TAC) is laminated on the other surface of the polarizer. A liquid crystal display device comprising the polarizer of claim 4 as an upper plate and a lower plate polarizer. The liquid crystal display of claim 6, wherein the liquid crystal display device is a twisted nematic (TN) mode in a normal white mode and an O-mode. The liquid crystal display device according to claim 6, wherein the liquid crystal display device includes a TN liquid crystal cell in which the liquid crystal alignment direction of the backlight side liquid crystal substrate is 135 degrees with respect to the horizontal direction and the liquid crystal alignment direction of the visual side liquid crystal substrate is 45 degrees To the liquid crystal display device. The liquid crystal display device according to claim 6, wherein the absorption axis of the polarizer of the lower plate polarizer is positioned at 135 degrees with respect to the horizontal of the backlight-side liquid crystal substrate when viewed from the viewer side. The liquid crystal display device according to claim 6, wherein the polarizing plate is configured to be orthogonal to the absorption axis of the polarizer and the slow axis of the discotic liquid crystal coating layer.

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